Method of manufacturing a twisted segmented finned tube

ABSTRACT

A method of manufacturing a twisted segmented finned tube is disclosed in which the method comprises the steps of feeding a continuous strip of flat coil stock from a roll onto a threestage roll former which progressively bends the one edge of the flat stock to form an L-shaped strip having a major fin portion and a continuous base portion oriented perpendicular thereto. The L-shaped strip is then fed into an apparatus which simultaneously cuts and twists the major fin portion of the stock to form segmented twisted fins thereon. The stock is then helically wound onto a tube with the base portion being continuously welded thereto by a weld wheel.

United States Patent Boose [54] METHOD OF MANUFACTURING A TWISTED SEGMENTED FINNED TUBE [72] Inventor: Robert Carl Boose, Pryor, Okla.

[73] Assignee: Escoa Flntube Corporation, Pryor, Okla. [22] Filed: Jan. 26, 1970 [21] Appl. No.: 5,782

[52] 0.8. CI ..219/107, 29/157.3 AH, 29/DIG. 18, 29/D1G. 48, 113/118 A, 219/83 [51] 1nt.Cl. ..B23k 9/02, 823k 1l/02,B23k 11/04 [58] Field of Search ..29/157.3 AH, D16. 18, DIG. 48; 113/118 A; 219/83, 107

[56] References Cited UNITED STATES PATENTS 2,251,642 8/1941 Tilley ..29/157.3 AH X 2,553,142 5/1951 McCreary ..29/157.3 AH 3,288,209 11/1966 Wall et a1. 29/157.3 AH X 3,362,058 1/1968 Morris et a1 ..29/157.3 AH

[ 1 Mar. 28, 1972 2,372,795 4/1945 Rodeck "113/118 A 2,965,744 12/1960 Busse ..219/107 3,427,427 2/1969 Rudd ..219/107 3,578,165 5/1971 Boose ..219/107 Primary Examiner-John F. Campbell Assistant Examiner-Donald C. Reiley, lll Attorney-Jackson and Jones [57] ABSTRACT A method of manufacturing a twisted segmented finned tube is disclosed in which the method comprises the steps of feeding a continuous strip of flat coil stock from a roll onto a threestage roll former which progressively bends the one edge ofthe flat stock to form an L-shaped strip having a major fin portion and a continuous base portion oriented perpendicular thereto. The L-shaped strip is then fed into an apparatus which simultaneously cuts and twists the major fin portion of the stock to form segmented twisted fins thereon. The stock is then helically wound onto a tube with the base portion being continuously welded thereto by a weld wheel.

4 Claims, 4 Drawing Figures PATENTEDMMBIQR 3,652,820

sum 1 BF 2 INVIiNI'IIR. Palmer 6m 0052- METHOD OF MANUFATURING A TWISTED SEGMENTEI) lFllNNElD TUBE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to finned tubing utilized in heat exchange apparatus and more particularly to the method of manufacturing a twisted segmented finned heat exchange tube.

- 2. Description of the Prior Art Tube type heat exchangers are used in a wide variety of applications for transferring heat from one fluid to another. For example, a plurality of tubes may be arranged within a casing in a parallel configuration for extracting heat from the hot exhaust gases of turbines. In this application water is normally circulated in the tubes while the hot exhaust gases are circulated over the external surface of the tubes. Such exhaust heat recovery systems generally dictate the use of extended heat transfer surfaces. Moreover, the high temperatures encountered dictate the use of relatively thick fin stock in forming the extended heat transfer surfaces.

The conventional tubing having extended heat transfer surfaces in finned tubing is manufactured in a variety of configurations. Various type fins include: a flanged fin type in which a major fin portion has a bottom flanged base oriented perpendicular thereto; a channel fin type in which a continuous base has a pair of fin portions extending radially upward therefrom in a U-shaped configuration; and an l-type fin in which a flat fin portion has its lower edge forming the base for connection to the tube. I

Each of these various fins can be of the continuous or segmented type. The continuous fins normally have a smooth continuous surface, although it could also be perforated to meet certain design conditions. The segmented fins are either oriented parallel to the root portion of the fin or are twisted at an angle thereto in any desired orientation in order to promote turbulence and increase the heat transfer rates. These fins may be engaged to the tube in a helical or longitudinal configuration with the method of securing the fins to the tube usually done by some type of welding or brazing.

A type of fin being used more extensively is the twisted segmented fin, helically wrapped around the tube. These twisted segmented finned tubes have not been commercially available to any great extent because of the shortcomings involved in the manufacturing of such tubes. Heretofore, these fins were usually serrated or out prior to being helically wound and bonded to the tube. The fins were then twisted in a separate operation after the stock was bonded to the tube. The difficulty with such a method arises in the twisting operation. Such an operation is usually done by hand, which is costly and time consuming. Moreover, the automatic machines that carry out this function are very expensive while still operating at a very slow rate. As a result, the costly and time consuming production methods of manufacturing such a fin tube severely restrict its widespread use.

SUMMARY OF THE INVENTION The present invention obviates the above-mentioned shortcomings by providing a method of manufacturing a twisted segmented finned tube that is simple, economical and rapid. The method includes steps of feeding a continuous strip of flat rolled stock from a roll onto a three-stage roll former, which progressively bends the one edge of the flat stock to form an L-shaped strip having a major fin portion and a continuous base portion oriented perpendicular thereto. The L-shaped strip is then fed onto an apparatus which simultaneously cuts and twists the major fin portion of the strip to form a plurality of segmented twisted fins. The stock is then helically wound onto a tube with the base portion being continuously welded to the tube by a weld wheel.

The main advantage of the present invention is that the cutting and twisting of the tin is done in a single operation,

prior to wrapping and bonding the stock to the tube. In this manner the operation can be accomplished with one machine. Moreover, since the cutting and twisting of the stock is done prior to the welding operation the cutting and twisting operation can be carried out more easily and efi'iciently.

Another advantage of the present invention is that the finned tube can be manufactured more rapidly and more economically. Moreover, the stock can still be welded to the tube by means of welding wheel which forms a continuous weld at the base of the fin. Such a welding process gives the strongest bond and is more preferable than a brazing operation.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 11 is a side elevational view of a twisted segmented finned tube constructed in accordance with the present invention;

FIG. 2 is a schematic view of the apparatus for manufacturing the segmented twisted finned tubing;

FIG. 3 is a sectional view of the coil stock taken along lines 3-3 of FIG. 2; and

FIG. 4 is a fragmentary view of the fin taken along lines 4- (i of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 11, there is shown a heat exchange tube 10 which may be made, for example, of steel with an L- shaped radially extending fin 12 welded to the outer portion of the tube. The fin 12 comprises a major fin portion [4 and a foot or base portion 16 extending perpendicularly thereto. The base portion 16 is welded to the outer periphery of the tube 10 by a continuous weld. The fin element 12 is wound in a spiral form along the length of the tube 10 forming, in effect, a series of segmented fins extending at right angles to the outer surface of the tube. The segmented fins 14 are also twisted at an angle, no more than 35, from the root portion thereof. When helically wrapped around the tube 10, the twisted segmented fins M are oriented in such a manner to promote turbulence and increase the heat transfer rate.

Segmented fins may be provided with any convenient spacing between turns within the limits of the forming and welding apparatus. The fin 12 may be formed from any desired gauge of metal up to the limit of the forming and cutting capabilities of the apparatus. For example, the tin may be formed from a strip of suitable metal, such as steel, having a thickness in the range from 12-50 thousandths of an inch. The foot portion need only be wide enough, i.e., 3/ 16 of an inch or less, to provide a sufficient lateral surface to be welded to the tube by the weld wheel of the welding machine, as will be described hereinafter in more detail.

The base portions of adjacent turns may abut against each other along the length of the tube or they may overlap.

Referring now to FIG. 2, there is illustrated a process for helically forming and welding an L-shaped metal strip 12 around the tube 10. The metal strip originates from a flat coil stock strip 20 being continuously supplied from a roll 21. The flat stock strip 20 is fed into a forming assembly indicated generally at 23. The forming assembly 23 includes three pairs of rotatably supported forming wheels which progressively bend the flat coil stock strip into an L-shaped metal strip 25 having a major fin portion 26 and a base portion 27 extending perpendicularly thereto, as shown in FIG. 3.

The L-shaped metal strip 25 is then fed into a cutter-twister forming assembly 30 which comprises a pair of cylindrical members 31 having cutting teeth 32 formed thereon to automatically cut the major fin portion of the strip traveling therebetween and twist the segmented fin formed thereby. A perspective view of the fin having the segmented fins l4 and the perpendicular base portion 16 is shown in F IG. 4.

The L-shaped strip is then fed onto a machine for helically forming and welding the L-shaped strip around the tube 10. A driving unit (not shown) is connected to one end of the tube to rotate the tube, for example, in a clockwise direction while simultaneously pulling the tube along a track and past a welding station indicated generally at 40. The welding station includes a weld wheel 41 rotatably mounted on a support. A ground wheel (not shown) is also rotatable mounted on a support and engages the tube in advance of the weld wheel. An alternating current source is connected between the weld and ground wheels through a switch (not shown) in a conventional manner. Tubes of fifty of more feet in length may be handled by the apparatus of FIG. 2 with a provision of a suitable number of support stations located on either side of the welding station.

in operation, the free end of the L-shaped strip 25 is fed onto the tube adjacent the weld wheel 41 and the base portion of the free end is spot welded to the tube by the weld wheel 41. The driving end (not shown) is then actuated to turn the tube in a clockwise direction to simultaneously pull the tube 10 in a direction parallel to its longitudinal axis past the weld wheel 41. The strip 25 is then further fed onto the tube with the driving unit continuing to rotate the tube 10 through a predetermined angle until the strip is adjusted to the corrected helical pitch. At this time the welding wheel 41 is energized to initiate the continuous welding operation. The angle through which the tube is rotated may be sufficient, for example, to provide one complete turn of the strip around the tube. The step of initiating the continuous welding operation only until the fin has been wound to a predetermined angle eliminates the necessity of precisely lining up the initial weld to insure a uniform pitch for the welded fin. After the tube 10 has been wrapped with the desired length of fin stock the tube may be removed from the welding machine and the initial unwelded removed from the tube to provide a tube with a uniform helically wrapped radial fin. The method and apparatus described above provides a durable, twisted, segmented finned tube with good heat transfer characteristics between the fin and the tube with the use of a relatively inexpensive apparatus.

While there has been shown but one preferred embodiment of the method for carrying out this invention, modifications and alterations will be apparent to those skilled in the art without departing from the scope and spirit of the invention.

What is claimed is:

1. A method of manufacturing a segmented finned tube comprising the steps of:

continuously supplying a flat coil stock strip;

forming the stock strip into an L-shaped strip having an elongated leg and a perpendicularly extending base prior to mounting the strip onto the tube; simultaneously cutting vertical slits along the length of the elongated leg portion substantially to the base of said leg portion to form a plurality of segmented fins, and twisting the segmented fins prior to welding the base to the tube;

mounting the continuous base onto the surface of the tube after the fins have been cut and twisted;

applying a welding current to the base and the tube as the base is being mounted on the tube; and

applying a forging force to the base as the current is being applied to create a fused bond between the base and the tube.

2. The method as defined in claim 1 wherein the stock strip is fed into a plurality of base forming rollers each pair of which progressively bends the strip until the base is perpendicular to the leg.

3. The method as defined in claim 1 wherein the L-shaped stri is fed between a pair of rollers having interengaging cu mg edges formed thereon for cutting and twisting the strip into a plurality of twisted segmented fins.

4. The method as defined in claim 1 wherein the step of welding the base of the strip to the tube comprises directing the base of the strip under a weld wheel and conducting welding current from the weld wheel through the base and the portion of the strip, that is from the point at which the con- 4 tubetinuous welding operation begins, and the first end may be i I I i l 

1. A method of manufacturing a segmented finned tube comprising the steps of: continuously supplying a flat coil stock strip; forming the stock strip into an L-shaped strip having an elongated leg and a perpendicularly extending base prior to mounting the strip onto the tube; simultaneously cutting vertical slits along the length of the elongated leg portion substantially to the base of said leg portion to form a plurality of segmented fins, and twisting the segmented fins prior to welding the base to the tube; mounting the continuous base onto the surface of the tube after the fins have been cut and twisted; applying a welding current to the base and the tube as the base is being mounted on the tube; and applying a forging force to the base as the current is being applied to create a fused bond between the base and the tube.
 2. The method as defined in claim 1 wherein the stock strip is fed into a plurality of base forming rollers each pair of which progressively bends the strip until the base is perpendicular to the leg.
 3. The method as defined in claim 1 wherein the L-shaped strip is fed between a pair of rollers having interengaging cutting edges formed thereon for cutting and twisting the strip into a plurality of twisted segmented fins.
 4. The method as defined in claim 1 wherein the step of welding the base of the strip to the tube comprises directing the base of the strip under a weld wheel and conducting welding current from the weld wheel through the base and the tube. 